1. Field of the Invention
The present invention relates to a dental application body, comprising an oxide ceramic, containing a bulk material containing an oxide ceramic and at least one coating. Furthermore, the invention relates to a method for producing such a dental application body by providing the bulk material, applying at least one coating, and by sintering the dental application body and the coating.
2. Description of the Related Art
The use of ceramic prostheses in dental application is known for many years, and the applications for sintered products encompass dental implants, bridges, abutments or the like. In general and compared to metal materials, ceramic material have improved properties, in particular with respect to strength, body compatibility, and have usually a color almost like the denture surrounding the implant. A further advantage of ceramic material used as dental implants is its low heat conductivity. Long-term studies, however, reveal that these ceramic materials are subject to aging, and that the fatigue strength of the material is of major importance. Especially when used as an implant replacing molar teeth, the implant has to provide a sufficient resistance to repeated stress over a time period of more than ten years without falling under a specific threshold value for their strength.
Especially when using zirconia ceramics, the effect of the tetragonal to monoclinic transformation of zirconia ceramics stabilized with 3 mol-% yttria has a detrimental effect on aging resistance and has already been investigated. For instance, Jérôme Chevalier et al. have described the significant effect of the presence of a cubic phase in hip prosthesis in the article “Critical effect of cubic phase on aging in 3 mol-%-yttria-stabilized zirconia ceramic for hip replacement prosthesis”, issued by Elsevier, Biomaterials, in the year 2004.
Blanks made from zirconium oxide ceramic are for instance disclosed in EP 1 210 054 using a mixture mainly comprising zirconium oxide, and minor amounts of hafnium oxide, yttrium oxide as well as oxides of aluminium, gallium, germanium, indium and the like. These blanks have a pore volume of between 50 and 65% and a pore size in the area of between 0.1 and 3 micrometers. The mixture is preformed into a desired shape, particularly by pressing the material into the blank form, and subsequently sintered in a temperature range of between 850 and 1000° C.
In the field of dental implants, ceramic materials provide the possibility of applying a coating on top of a bulk, wherein this coating has an increased porosity with respect to the bulk material. This more porous structure at the outer surface of the implant provides for a bigger surface, thus resulting in an improved osseointegration of the implant itself.
Among those porous coatings that have been developed or tested by the applicant, certain embodiments showed particularly advantageous results. For example, a specific coating contains zirconium oxide as a main component in some embodiments.
Preventing aging of the dental implant's material is of major importance for the producers of dental implants made of ceramics. Aging may lead to decreased fatigue strength of the implant or at least its surface, possibly resulting in parts of the implant's surface flaking off the implant body.
Tests performed with ceramic bodies coated with a porous outer layer, however, revealed that, under specific circumstances, such coating may lead to an accelerated aging performance of at least the interface between the bulk and a coating.